First of all, it is currently considered sacred text. On one of my readings of it I felt there was a lesson there about a girl from the countryside being offered all the incredibly rich and powerful Solomon could offer, if she would just become a member of his intimate family. But she being true to a shepherd who loved her, refused those worldly offers and remained true to her shepherd---just as Christians are asked to live lives true to their loving shepherd Jesus Christ.
I have meditated on this deeply, and I believe that the Divine had a very specific intention in including erotic poetry in the sacred texts of the Bible.
There is a life lesson for all of us, "for Love is as strong as Death." Love brings new life into being, so God's children continue to live, even though each of us is mortal. Let us realize that carnal love is part of God's gift of life to us all, and make it sacred in our use of it - to bring joy, and bring greater love into the world, as well as to bring children into the world.
Let us side with Love, so that with us on the side of Love, Love is stronger than Death.
'Sacred' is a human term that has much to do with culture; people decide and then hold traditions of what is 'sacred'. As for God being sexual, the reasoning/logic is this: if we are made in God's image and we are sexual, then so is God.
It is sacred text. It should be held sacred by all who profess a belief in the Bible. It should not be spoke of lightly either because it speaks of the most holy sacrament sanctioned by God to man, sex.
Sexual relationships in marriage are holy and thus are to be keep out of the media and mouths of people in such matter of fact tones.